Secure distance computation is performed when there are privacy constraints on one or both the signals. One way to solve this problem is to use encryption functions that allow computation in the ciphertext space. Such cryptosystems are called homomorphic cryptosystems. Many protocols based on homomorphic cryptosystems have been developed. Applications include secure computing, wherein a client processor can send encrypted data to a server. The server interacts with the client to solve a mathematical problem without revealing data to untrusted third parties. The protocols include, among other things, polynomial function computation primitives, which allow computation of Euclidean distance (L2 norm), L3 norm, correlation, etc. However, there are no efficient protocols for computing the absolute distance between pairs of signals under privacy constraints.
Accordingly, there is a need for a method for determining an absolute distance between two signals such that this method is suitable for secure computation of such an absolute distance.